You can cancel any contract any time you want, as long as it's done in writing. That's how it works for any insurance contract, including whatever the hell work-based insurance is.
The only question is how much it will cost you. Non-renewing your insurance (letting it expire) usually costs nothing, but there is almost always a cancellation fee for mid-term cancellation. They don't call it a cancellation fee, they call it "short rate cancellation earned premium", but it's a cancellation fee.
How much the fee will be depends on the insurance company, the type of policy and where you live, all of which you didn't say. The amounts vary widely based on those factors, but it's usually more than cancelling a newspaper subscription but less than cancelling a gym membership or cell phone contract.